Sandwich structure SiCf/Si3N4-SiOC-Si3N4 composites for high-temperature oxidation resistance and microwave absorption

SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) have been widely used as structural-functional materials at high temperatures. However, their mechanical and electromagnetic wave (EMW) absorbing properties will deteriorate due to high-temperature oxidation. Therefore, unique sandwich structure, consisting of inner Si3N4 impedance layer, middle porous SiOC loss layer and dense oxidation-resistant Si3N4 layer, was proposed to enhance multiple material properties in oxidation environment. Herein, SiCf/Si3N4 -SiOC-Si3N4 composites was fabricated by alternating chemical vapor infiltration (CVI) and polymer infiltration pyrolysis (PIP) methods. For these composites, SiC fiber is used as both reinforcing phase and electromagnetic (EM) absorber. CVI Si3N4 matrix was distributed in inner and outer layer of the SiCf /Si3N4-SiOC-Si3N4 composites. While inner Si3N4 layer between BN interphase and SiOC matrix forms nano-heterogeneous interphase to consume EM energy and enhance mechanical properties of composites, outer dense and oxidation-resistant CVI Si3N4 coating serves to maintain properties. PIP SiOC matrix exhibits porous structure that can effectively deflect cracks and achieve multiple scattering of EMW. SiCf/Si3N4-SiOC-Si3N4 composites with sandwich structure demonstrated excellent EMW absorbing properties and mechanical performance in high-temperature oxidation environments.